The document is about finding the number of prime numbers between 80 and 90. It defines f(x) as the number of primes less than or equal to x. It then states that the primes between 80 and 90 are 83 and 89. Therefore, the value of f(90) - f(80) is 2.

1. Number Theory

2. Number Theory
If f(x) is the number of primes less than or equal to x, find the value
of f(90) - f(80) = ?
(a) 3 (b) 2
(c) 1 (d) 4

3. Number Theory
Solution:
f(90) - f(80) = Number of primer between 90 and 80.
Listing, we have 83 and 89.
f(90) - f(80) = 2
Answer Choice (B)
If f(x) is the number of primes less than or equal to x, find the value
of f(90) - f(80) = ?

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